<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      * {
        margin: 0;
        padding: 0;
      }

      .box {
        width: 400px;
        position: relative;
        margin: 50px;
      }

      .middle {
        width: 400px;
        height: 400px;
        border: 1px solid #000000;
      }
      .middle img {
        width: 100%;
        height: 100%;
      }
      .shadow {
        width: 100px;
        height: 100px;
        background: rgba(255, 255, 0, 0.5);
        position: absolute;
        left: 0;
        top: 0;
        display: none;
      }

      .small {
        display: flex;
        justify-content: flex-start;
      }
      .small a {
        width: 52px;
        height: 52px;
        margin: 10px 10px;
      }
      .small img {
        height: 100%;
        border: 1px solid green;
      }

      .enlarge {
        width: 400px;
        height: 400px;
        border: 1px solid #333333;
        position: absolute;
        top: 0;
        left: 105%;
        background-image: url(./images/2.big.jpg);
        background-position: 0 0;
        background-repeat: no-repeat;
        background-size: 800px 800px;
        display: none;
      }

      .small img.active {
        border-color: red;
      }
    </style>
  </head>
  <body>
    <div class="box">
      <!-- 中等图 -->
      <div class="middle">
        <img src="./images/1.jpg" alt="" />
        <!-- 遮罩 -->
        <div class="shadow"></div>
      </div>
      <!-- 小图 -->
      <div class="small">
        <a href="#"><img class="active" src="./images/1.small.jpg" alt="" /></a>
        <a href="#"><img src="./images/2.small.jpg" alt="" /></a>
      </div>
      <!-- 放大图 -->
      <div class="enlarge"></div>
    </div>

    <script>
      // 构造函数
      function Enlarge(classname) {
        // 获取到需要操作的元素
        this.box = document.querySelector("." + classname);
        this.middle = this.box.querySelector(".middle");
        this.middleImg = this.middle.querySelector(".middle img");
        this.shadow = this.middle.querySelector(".middle .shadow");
        this.smallImgs = this.box.querySelectorAll(".small img");
        this.enlarge = this.box.querySelector(".enlarge");
        var _this = this;
        // 小图片绑定点击切换事件
        for (var i = 0; i < this.smallImgs.length; i++) {
          this.smallImgs[i].onclick = function () {
            _this.tab(this);
          };
        }
        // 给middle绑定鼠标划入事件
        this.middle.onmouseover = function () {
          _this.over();
        };
        // 给middle绑定鼠标划出事件
        this.middle.onmouseout = function () {
          _this.out();
        };
        // 给middle绑定鼠标移动事件
        this.middle.onmousemove = function () {
          _this.move();
        };
      }
      //小图片点击切换方法
      Enlarge.prototype.tab = function (ele) {
        var active = this.box.querySelector(".small img.active");
        active.className = "";
        ele.className = "active";
        // 获取图片后缀,通过获取 . 的下标，然后截取后缀
        var dIndex = ele.src.lastIndexOf(".");
        console.log();
        var suffix = ele.src.slice(dIndex);
        console.log(suffix);
        console.log(this);
        // 改变中等图片
        this.middleImg.src = "./images/2" + suffix; //1.jpg  2.jpg
      };
      // 鼠标划入显示方法
      Enlarge.prototype.over = function () {
        this.shadow.style.display = "block";
        var dIndex = this.middleImg.src.lastIndexOf(".");
        var suffix = this.middleImg.src.slice(dIndex - 1);
        this.enlarge.style.backgroundImage = `url(./images/1.big.jpg)`;
        this.enlarge.style.display = "block";
      };
      // 鼠标划出隐藏方法
      Enlarge.prototype.out = function () {
        this.shadow.style.display = "none";
        var dIndex = this.middleImg.src.lastIndexOf(".");
        var suffix = this.middleImg.src.slice(dIndex - 1);
        this.enlarge.style.backgroundImage = `url(./images/${suffix})`;
        this.enlarge.style.display = "none";
      };
      // 鼠标滑动让遮罩和大图对应移动的方法
      Enlarge.prototype.move = function (e) {
        var e = e || window.event;
        // 获取鼠标的坐标
        var x = e.clientX;
        var y = e.clientY;
        // box相对浏览器的偏移值
        var boxLeft = this.box.offsetLeft;
        var boxTop = this.box.offsetTop;
        // 获取遮罩一半的宽高，让光标可以在中间
        var boxW = this.shadow.clientWidth / 2;
        var boxH = this.shadow.clientHeight / 2;
        console.log(boxW, boxH);
        // 限制左上角移动的边界
        if (x < boxLeft + boxW) {
          x = boxLeft + boxW;
        }
        if (y < boxTop + boxH) {
          y = boxTop + boxH;
        }
        // 限制右下角移动的边界值
        if (x > boxLeft + this.middle.clientWidth - boxW) {
          x = boxLeft + this.middle.clientWidth - boxW;
        }
        if (y > boxTop + this.middle.clientWidth - boxH) {
          y = boxTop + this.middle.clientWidth - boxH;
        }
        // 用获取到的值设置遮罩的left和top值，让它移动
        this.shadow.style.left = x - boxLeft - boxW + "px";
        this.shadow.style.top = y - boxTop - boxH + "px";

        // 让大图移动
        // 计算遮罩和中盒子的比例
        var xPercent = this.shadow.offsetLeft / this.middle.clientWidth;
        var yPercent = this.shadow.offsetTop / this.middle.clientHeight;
        // 获取大图的宽高大小
        var enlargeBgWidth = parseInt(
          window.getComputedStyle(this.enlarge)["background-size"].split(" ")[0]
        );
        var enlargeBgHeight = parseInt(
          window.getComputedStyle(this.enlarge)["background-size"].split(" ")[1]
        );
        // 计算大图要移动的距离
        var xMove = enlargeBgWidth * xPercent;
        var yMove = enlargeBgHeight * yPercent;
        // 将要移动的距离设置到背景图定位的left和top值上，让大图移动
        this.enlarge.style.backgroundPosition = -xMove + "px " + -yMove + "px";
      };
      // 实例化
      var enlarge = new Enlarge("box");
    </script>
  </body>
</html>
